Phase discriminating apparatus



y 3, 1960 T. A. PATCHELL 2,935,660

PHASE DISCRIMINATING APPARATUS Original Filed July 9, 1954 2 Sheets-Sheet 1 INVENTOR.

ATTORNEY.

THOMAS A PATCHELL MOTOR VOLTAGE F I G. 3

SIGNAL VOLTAGE |ao OUT a E. (mo) NO SIGNAL LINE VOLTAGE LINE VOLTAGE IN PHASE WITH OF PHASE WITH May 3, 1960 'r. A. PATCHELL PHASE DISCRIMINATING APPARATUS Original Filed July 9; 1954 2 Sheets-Sheet 2 FIG.8

E 2 A 0A TT W V HE HE L H6 6 LE A W G N T U T MA 6 M 0am GU s V MVAV SO HE v M MM m l FL M 0 FIG.6

INVENTOR. THOMAS A. PATCH ELL 0 SIGNAL m PHASE WITH OUT VOLTAGE LINE VOLTAGE fi E QSE Zg RELAY 79' RELAY 7B ATTORNEY.

United States Patent PHASE DISCRINHNATING APPARATUS Thomas A. Patchell, Havertown, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Original application July 9, 1954, Serial No. 442,290. Divided and this application November 8, 1956, Serial No. 621,109

Claims. (Cl. 317-1485) There are certain applications for which transistors,

by virtue of their operating characteristics, areextremely Well suited. Among these are applications in which they perform a switching operation which is characterized by a high impedance in one state and a low impedance in another state. Under certain conditions, the impedance of the collector to base circuit of a transistor can be made to exhibit such characteristics by controlling the magnitude and polarity of the voltage applied between the transistor emitter and base.

It is therefore another object of the present'invention to provide improved switching circuits employing the signal applied between the emitter and base of a transistor to control the impedance of the transistorcollector to base circuit. 1

Phase discriminating circuits are commonly employed in self-balancing measuring'and control apparatus toinitiate the rebalancing operation in response to a signal of one phase or the opposite phase with respect to a reference signal. In such an application they are generally required to deliver a usable amount of current to a motion producing element of the rebalancing mechanism which could be a relay, or a reversible motor. The amount of current required by such an element is often beyond that which a transistor can constantly deliver. When operated as a switching element, however, a transistor can deliver larger amounts of current, at low voltages, than it otherwise could deliver, because the transistor power dissipation is not constant over -the entire transistor operating range.

It is therefore still another object of the present invention to employ transistors as switching elements in phase discriminating circuits and thereby increase the amount of power which they can deliver to the load.

A further object of this invention is to provide new and improved transistor phase discriminating switching apparatus which are operative to initiate relay or reversible motor operation.

It is another further object of the present invention to provide new and improved transistor phase discriminating switching apparatus which are operative to produce output voltages having characteristics dependent upon the phase relationship between a control signal and a ref-' erence voltage.

A still further object of the present invention is to provide new and improved transistor phase discriminating apparatus in which the output voltage characteristic is dependent upon the phase relationship between a control signal and a reference voltage and is, in one form of the invention, the polarity of a pulsating unidirectional voltage; in another form of the invention, the

"ice

2 phase of a pulsating unidirectional voltage; and in still another form of the invention, the phase of an alternating voltage.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages, and the specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which are illustrated and described preferred embodiments of this invention.

Of the drawings:

Fig. l is a circuit diagram of an embodiment of the present invention designed to operate a pair of polarized relays selectively in response to the phase relationship between a control signal and a reference voltage;

Fig. 2 shows, for a point contact type transistor, a typical family of collector current vs. collector voltage curvesffor a series of constant values of emitter current;

Fig. 3 is a table showing, for various control signals, the wave form of the load voltage produced by the embodiment of this invention shown in Fig. 1;

Fig. 4 shows a circuit diagram of a modificationof the embodiment of the present invention shown in Fig. '1, adapted to operate a reversible D.C. motor;

Fig. 5 is a circuit diagram of another embodiment of this invention in which transistors are employed as shorting switches to control the operation of a pair of relays selectively in response to the phase relationship between a control signal and a reference voltage;

Fig. 6 is a table showing, for various control signals, the wave form of the load voltage produced .by the embodiment of this invention shown in Fig. 5;

Fig. 7 is a circuit diagram of another embodiment of the present invention which isadapted to provide full wave energization for a two phase reversible induction motor in response to the phase relationship between a control signal and a reference voltage; and

Fig. 8 is a table showing, for various control signals, the wave form of the load voltage produced by the embodiment of this invention shown in Fig. 7.

Referring first to Fig. 1, there is shown a circuit diagram of .an embodiment of this invention designed to operate a pair of polarized relays selectively in response to the phase relationship between a control signal and a reference signal. The point contact transistors 1 and 2 having the usual collector electrode, emitter electrode "and base electrode, are employed as the switching elements. Point contact transistors usually have current amplification factors greater than unity and are extremely well suited for use in the type circuits described in this specification. The switching control signal is applied to this circuit across the input terminals 3 and 4. The reference voltage is the voltage across the alternating current conductors L and L This voltage is introduced into the circuit across the secondary winding 5 of the transformer 6 having its primary winding 7 connected across the conductors L and L The emit- .ter 8 of the transistor 1 and the emitter 9 of the transistor 2 are both connected to the input terminal 3. The base 11 of the transistor 1 and the base 12 of the transistor 2 are both connected to the input terminal 4, which is grounded. The relays 13 and 14, polarized by the diodes 15 and 16 respectively, are connected in parallel with each other between the collector 17 of the transistor 1 and the end terminal 18 of the secondary winding 5 of the transformer 6. The other end terminal 19 of the secondary winding 5 is connected to the collector 20 of the transistor 2. The condensers 21 and 122 shunting the relays 13 and 14 respectively are smoothing condensers .for eliminating :relay chatter.

aesaeeo In considering the application of transistors to the phase sensitive switching circuits described in this specification, their operation can be best understood by thinking of them as controlled diodes. Under the conditions described below, the signal applied between the emitter and base of the transistor controls the impedance of its collector to base circuit. In the absence of such a signal, the impedance of the collector to base circuit depends upon the magnitude and polarity of the signal applied between the collector and base. If this latter signal makes the collector sufiiciently positive with respect to the base, the collector to base impedance will be low. Conversely, if this signal makes the collector negative with respect to the base, the impedance of that circuit will be high. A suitable signal applied between the emitter and base, such that the emitter is positive with respect to the base, will overcome the efiect of a negative collector to base signal and reduce the impedance of that circuit. A signal making the emitter negative with respect to the base, however, will have no appreciable efiect on that impedance.

If any circuit element is to be operated as a switch, that element should have the common property ascribable to the switching function, that of definiteness of state. Generally, switches are either open or closed with the intermediate region between these two positions characterized by time, that is, how fast does the switch go from one state to the other. This should be especially true when a transistor is operated as a switch. Referring to Fig. 2, there is shown, for a point contact type transistor, a typical family of collector current vs. collector voltage curves for a series of constant values of emitter current. On these curves, in dotted line, is also shown the curve for maximum collector power dissipation, which is a rectangular hypcrbola. For continuous operation any choice of operating point above it is not permissible. Limited by the peak inverse voltage rating of the transistor and the fact that beyond a certain value of collector current, the current amplification factor of the transistor will fall off, any load line below or tangential to this curve may be employed. Such a load line is shown and identified by the letter A. It should be noted, however, that with such a load line, a very limited current can be delivered to the load and that the back resistance of the collector to base circuit may not be very high. Under such operating conditions, a transistor would not be a very efiicient switching element.

When operated as a switching element, however, the collector power dissipation of a transistor is not constant and a load line bisecting the constant collector power dissipation line is permissible providing that operation in the area above that curve is momentary. Such a load line is indicated by the letter B. Under such conditions the sections of that load line, designated by the latter a, indicates the open positions of the switch where the collector to base impedance is high; the section of that load line designated by the letter 12 indicates the intermediate region between the closed and open positions, through which region the time of operation'is made as short as possible; and the section of that load line indicated by the letter c indicates the open position of the switch in which the collector to base impedance is low and the current delivered to the load is high. Thus, if the signal that is applied between the emitter and base of a transistor is of a suitable magnitude, such that the transistor switch is driven quickly between its closed and open positions, better switching action is obtained and a larger current can be delivered to the load. In the circuits shown in Fig. 1 and the other switching circuits considered in this specification the emitter to base control signal is considered to be of such a magnitude as to achieve this type of switching action.

In considering the specific operation of the circuit shown in Fig. 1, reference should be had to Fig. 3. For that purpose, the control signal, applied to the circuit between the input terminals 3 and 4, will be considered to be in phase with the line or reference voltage when the input terminal 3 has the same instantaneous polarity as the end terminal 18 of the secondary winding 5. With no control signal, very little current will flow through the load, namely, the polarized relays 13 and 14, during either half cycle of the reference voltage. This limited current flow is due to the high collector to base impedance of the transistor, which during the half cycle of line voltage under consideration, hasits collector biased negatively with respect to its base. During each half cycle of the line voltage, the collector of one of the transistors will have such a negative collector bias. When a suitable control signal, which is in phase or out of phase with the reference voltage, is applied across the input terminals 3 and 4, however, the emitters of both of the transistors will be positive for one half cycle when the collector of one of the transistors is biased negatively, and that transistor will conduct despite its negative collector bias, permitting a relatively large current to flow to the load.

If the control signal is in phase with the line voltage and if the input terminal 3 and thus the emitters of both transistors are positive during the first half cycle of the line voltage under consideration, a relative large cur rent will flow through the load during that half cycle. During that time, the collector 17 of the transistor 1 will be biased positively and the collector electrode 20 of the transistor 2 will be biased negatively by the voltage across the secondary winding 5. The current flow will be from the positive terminal 18 of the secondary winding 5, through the relay 13, the diode 15, the collector to base circuit of the transistor 1 and, because of the positive signal on the emitter 9, through the collector to base circuit of the transistor 2 to the negative terminal 19 of the secondary winding 5. During the next half cycle of the line voltage, the emitters of both transistors will be negative and the current flow through the load will be greatly reduced by the high impedance of the collector to base path of the transistor 1, which during that half cycle has its collector biased negatively with respect to its base. Thus, for a control signal signal in phase with the line voltage, the relay coil 13 will receive an energizing pulse on alternate positive half cycles.

If the control signal is 180 out of phase with the line voltage and if the input terminal 3 and thus the emitters of both transistors are negative during the first half cycle of the line voltage, a relatively small current will flow through the load during that half cycle. This limited current flow is due to the high impedance of the collector to base circuit of the transistor 2 which, during that half cycle, has its collector biased negatively with respect to its base. During the next half cycle, the emitters of both transistors will be positive, and a relative large current will flow from the positive terminal 19 of the secondary winding 5 through the collector to base circuit of the transistor 2, through the collector to base circuit of transistor 1, which, because of the positive signal on the emitter 3, will have a low impedance, through the diode 16, and through the relay coil 14 to the negative terminal 18 of the secondary winding 5. Thus, for a control signal 180 out of phase with the line voltage, the relay coil 14 will be energized on alternate negative halt cycles.

This circuit produces a pulsating unidirectional voltage across the relays 13 and 14 having a polarity depending upon the phase relationship between the control signal and the line or reference voltage. The condensers 21 and 22 shunting the relays 13 and 14 respectively, are provided to prevent the relays from chattering when so energized. These relays may be employed to control the operation of a reversible motor or to directly control an industrial process or rebalancing operation.

As shown in Fig. 4, the circuit of Fig. 1 can be adapted to perate a ma l di ect current motor. In this circuit,

.between a control signal and a reference voltage.

the reference voltage.

zaps-5,060

:theemitter 18 of the transistor :1 and the emitter '9 of the transistor 2 are connected to one end-terminalofthe secondary winding 30 of the input transformer 31. The base 11 of the transistor 1 and the base 12 of the'transistor'2 are connected'to the other end terminal of the secondary winding. 30. The input transformer 31 has a former 6 to the other input terminal of the filter 33. "Theoutput terminals of the filter 33 are connected to *thedirect current motor 34. The motor 34 may be a small permanent magnet .D.C. motor.

The use of the input transformer 31 permits the grounding of one terminal of-the'filter 33 which is desirable in many ap- 'plications.

The operation ofthis circuit is identical to the operation ofthe circuit shown in Fig. 1 except'that the voltage applied to the load is filtered and used to drive the motor 34. The direction of rotation of the motor 34 depends upon the polarity of the voltage applied thereto and hence the phase relationship between the control signal andthe reference voltage.

Referring now to Fig. 5, there is shown an embodimerit of this inventionin which transistors are employed as shorting switches to .control the operation of a pair of relays selectively in response to the phase relationship In this circuit the transistors '61 and 62 are the switching elements. The emitter 63 of the transistor 61 and the emitter 64 of the transistor 62 are both connected to the input terminal 65. The base 66 of the transistor 61 and the base 67 of the transistor 62 are both connected to the input terminal 68 which is grounded. The collector 71 of the transistor 66 is connected to the end terminal 72 of the secondary winding 73 of the transformer 74. The collector 75 of the transistor 62 is connected to the end terminal 76.of the secondary winding 73. The transformer 74 has a primary winding 77 connected across a suitable source of reference voltage, the alternating current conductors L and L The relay 78 is connected between the collector 71 and the base 66 of the transistor 61 and the relay 79 is connected between the collector 75 and the base 67 of the transister 62. As will be explained below, in the absence of a control signal the relays 78 and 79 are normally energized by a pulsating unidirectional current. To prevent chatter, the relays 78 and 79 are long time constant relays.

In considering the operation of the circuit ,shown .in Fig. reference should be had to Fig. .6. For that purpose, the control signal applied to the circuit between input terminals 65 and 68, will be considered in phase with the line or reference voltage when the input terminal 65 has the same instantaneouspolarity as :the

end terminal 72 of the secondary winding '73. With .no

phase with the reference voltage,,is applied between the input terminals 65 and 68, however, the emitter of one of the transistors will be biased positively during the half cycle when its collector is biased negatively, thereby reducing the impedance of its collector to base circuit, and thus causing that transistorto act as a short circuit bi-passing current around its relay.

If the control signal is in phase with the reference voltage, the input terminal 65 and the emitters Qfboth transistors Will be positive during the first half cycle of During that half cycle the 'endterminal 72 of the secondary winding 73 will be positive'and the end terminal 76 'of the secondary winding 73"will be negative and current 'will 'fiow *fromthe positive terminal 72 through the collector'to base -c'ircuit of the transistor 61 and through the collector to base circuit of the transistor 62, which, because of the positive bias on the emitter 64, will be low despite the negative bias on the collector 75, to the negative terminal 76 of the secondary winding 73. During the next half cycle the emitters of both transistors will be negative and the terminal 76 of the secondary winding 73 will be positive and the terminal 72 of the secondary Winding 73 will be negative. During this half cycle the current flow will be'from the positive terminal 76 through the collector to base circuit of the transistor 62 and, due to the high impedance of the collector of the base circuit of the transistor 61, through the relay 78. Thus, if the control signal is in phase with the line voltage, the relay 7% will not be energized during either'half cycle of the reference voltage, but the relay '78 will be energized on alternate half cycles.

If the control signal is 180 out of phase with the reference voltage, the input terminal and the emitters of both transistors will be negative during the first half cycle of the reference voltage. During that half cycle, the end terminal 72 of the secondary Winding 73 will be positive and the end terminal 76 of the secondary Winding 73 will be negative. The current will flow from the positive terminal 72 of the secondary winding 73 through the collector to base circuit of the transistor 61 and, because of the high impedance of the'collector to base circuit of the transistor '62 caused by the negative bias on its collector, through the relay 79' to the negative terminal 76 of the secondary winding 73. During the next half cycle, the emitters of both transistors will be positive and the end terminal 76 of the secondary winding 73 will be positive and the end terminal 72 of the secondary winding 73 will be negative. During thathalf cycle, current will flow from the positive terminal 76 of the secondary winding 73 through the collector of the base circuit ofthe transistor 62 and through the collector of the base circuit of the transistor 61 (which, because of the positive bias on the emitter 63, will have a low impedance despite the negative bias on the collector 71), to the negative terminal. 72 ofsecondary winding 73. Thus, if the control signal is 180 out of phase with the line voltage, the relay 78 will not be energized during either half cycle of the reference voltage, but the relay 79 will be energized on alternate half cycles.

As just described, the transistors Hand 62 function as shorting switches bypassing the current around the relays 7,8 and 79 respectively, in accordance with the phase relationship between the control signal and the reference voltage. If the control signal is in phase with the reference voltage, relay 79 will be deenergized and it the signal is 180 out of phase with the reference voltage, the relay 78 will be deenergized. In the absence of any controlsignal both relays are energized on alternate half cycles by pulses of unidirectional current.

Referring now to Fig. 7 thereis showna modification of this invention employed in a self balancing measuring apparatus adapted to measure theresistance of the temperature sensitive resistor 80. In this apparatus, changes in theresistance of the resistor 80 unbalance the Wheatstone bridgemeasuring circuit 81. This unbalance is amplified by means of the electronic amplifier'82 which is operative to impress upon the phase discriminating switching circuit 83 a signal varying in magnitude and phase in accordance with the magnitude and direction of unbalance. The switching circuit 83, in turn, operates selectively, in accordance with the phase and magnitude of this signal, to energize the rebalancing motor 84 driving it in a direction and to the extent necessary to re- .balance themeasuring circuit 81.

The Wheatstone bridge circuit 81 comprised of two branches connected in parallel across the secondary winding 85' of the transformer86. 'One'of these branches comprises the slidewire resistor 87 and the other branch comprises the temperature sensitive resistor 80 and the resistor 89. The sliding contact 92 engages the slidewire 87 and is adjustable along the length of the latter by means of the rebalancing mechanism 93 which is operated by the reversible motor 84. The transformer 86 has a primary winding 94 which is connected to a suitable source of alternating current, the conductors L and L Bridge unbalance is measured between the junction 95 of the resistors 80 and 89 and the sliding contact 92 on the slidewire resistor 87, which points are connected to the input terminals of the electronic amplifier 82 by the leads 96 and 97.

The electronic amplifier 82 may be any suitable alternating current amplifier capable of amplifying bridge unbalance to the extent necessary for initiating switching action in the phase sensitive switching circuit 83. The output of the amplifier 82 is connected to the primary winding 101 of the input transformer 102 of the phase discriminating switching circuit 83.

The phase discriminating circuit 83 employs as its switching elements the transistors 103, 104, 105, and 106 each having the usual collector electrode, emitter electrode and base electrode. The switching control signal is applied to this circuit by means of the input transformer 102 which has two secondary windings 107 and 108. The secondary winding 107 has end terminals 111 and 112 and a center tap 113. Secondary winding 108 has end terminals 114 and 115 and a center tap 116. The emitter 117 of the transistor 103 is connected to the end terminal 111 of the secondary winding 107 and the emitter 118 of the transistor 104 is connected to the end terminal 112 of the secondary winding 107. The base 121 of the transistor 103 and the base 122 of the transistor 104 are connected to the center tap 113 of the secondary winding 103. Similarly, the emitter 123 of the transistor 105 is connected to the end terminal 114 of the secondary winding 108 and the emitter 124 of the transistor 106 is connected to the end terminal 115 of the secondary winding 108. The base 125 of the transistor 105 and the base 126 of the transistor 106 are connected to the center tap 116 of the secondary winch ing 108. The collector 127 of the transistor 103 is connected to the end terminal 128 of the secondary winding 129 of the transformer 131. The collector 132 of the transistor 106 is connected to the end terminal 133 of the secondary winding 129. The secondary winding 129 has a center tap 134 which is connected to the collectors 136 and 137 of the transistors 104 and 105 respectively through the parallel circuit comprising the condenser and the motor control winding 135 of the reversible two phase induction motor 84. The transformer 131 has a primary winding 138 which is connected across the conductors L and L As shown, the rebalancing motor 84 is a two phase reversible induction motor having, in addition to the motor control winding 135, a rotor 141 and a power winding 142. The power winding 142 is connected to the condenser 143 to conductors L and L The rotor 141 of the rebalancing motor 84 is operative through the gear train 93 to adjust the sliding contact 92 of the rebalancing slidewire 87 of the Wheatstone bridge circuit 81.

The direction of rotation of the rebalancing motor 84 depends upon the phase relationship between the current in the control winding 135 and the current in the power winding 142. The condenser 140 is selected with respect to the motor control winding 135 so as to form therewith a substantially parallel resonant circuit. Current flowing through this parallel resonant circuit is in phase with the voltage across it but the current through the motor control winding 135 lags that voltage by approximately 90. The condenser 143 is selected with respect to the power winding 142 so as to form therewith a substantially series resonant circuit. Due to this series resonant circuit, the current flow through the power winding 142 is-in phase with the reference voltage, the voltage across the conductors L and L Thus, if the voltage across the control winding 135 is in phase with the reference voltage, the motor 84 will rotate in one direction and if the voltage across the control winding 135 is 180 out of phase with the reference voltage the motor 84 will rotate in the other direction.

Before considering the operation of the self balancing measuring apparatus as a whole, the specific operation of the phase discriminating switching circuit 83 will be explained. For this purpose, reference should be had to Fig. 7. The control signal applied to the circuit through the input transformer 102 will be considered to be in phase with the reference voltage when the end terminals 111 and 114 of the secondary windings 107 and 108 respectively have the same instantaneous polarity as the end terminal 128 of the secondary winding 129 of the transformer 131. The switching circuit 83 can be considered as comprising two separate switching circuits, one operative to energize the motor control winding 135 when the control signal is in phase 'with the reference voltage and the other operative to energize the motor control winding 135 when the control signal is 180 out of phase with the line voltage. One of these two switching circuts is designated by the numeral 98 and employs the transistors 103 and 104. The other of these circuits is designated by the numeral 99 and employs the transistors and 106.

In the absence of a control signal, no current will flow through the motor control winding 135 because the impedance of both switching circuits will be equal and it will appear as a balanced bridge impressing no voltage across the winding. During one half cycle of the reference voltage the end terminal 128 of the secondary winding 129 will be positive with respect to the center tap 134 and the transistor 104 will have its collector biased negatively with respect to its base. During that half cycle, the end terminal 133 of the secondary winding 129 will be negative with respect to the center tap 134 and the transistor 106 will have its collector biased negatively with respect to its base. During the next half cycle of the reference voltage, the end terminal 128 of the secondary winding 129 will be negative with respect to the center tap 134 and the transistor 103 will have its collector biased negatively with respect to its base. During that half cycle, the end terminal 123 of the secondary winding 129 will be positive with respect to the center tap 134 and the collector of the transistor 105 will be biased negatively with respect to its base electrode. Thus, during each half cycle of the reference voltage and in the absence of a control signal, one of the transistors in each switching circuit will have a low collector to base impedance and the other transistor will have a high collector to base impedance thereby making the impedance of both circuits equal.

When a control signal in phase with the reference voltage is applied to the input transformer 102, the end terminal 111 of the secondary winding 107 will be positive with respect to the end terminal 112 and the end terminal 114 of the secondary winding 108 will be positive with respect to the terminal during the first half cycle of the reference voltage under consideration. During this half cycle, the end terminal 128 of the secondary winding 129 will be positive with respect to the center tap 134 and the terminal 133 will be negative with respect to the center tap 134. Very little current will flow in the switching circuit 98 because of the negative collector to base and emitter to base bias voltage on the transistor 104. However, a large current will flow in the switch ing circuit 99. The direction of this current flow will be from the center tap 134 of the secondary winding 129 through parallel combination of the motor control Winding and the condenser 140, through the collector to base circuit of the transistor 105, and through the collector to base circuit of the transistor 106 (which will have 'a ,low collector to base impedance, despite its negative collector bias, because of the positive signal on its emitter), to the negative terminal 133 of the secondary winding 129. During the 'next half cycle, the respective collector and emitter biases will'be reversed. Very little current will flow in the switching circuit 98 because of the negative collector to base and emitter to base bias trol winding 135 and the condenser 140 to the center tap 134. Thus, when the control signal is in phase with phase discriminating circuit 83 will 'energizethe motor control winding 135 with a 60 cycle alternating current *which will lag the reference voltage by approximately When a control signal 180 out of phase with the reference voltage is applied to the input transformer 102, the end terminal 111 of the secondary winding 107 will be negative with respect to the end terminal 112 and the end terminal 1150f the secondary winding 108 will be negative with respect to the end terminal 114 during the first half cycle of the reference voltage under consideration. secondary winding 129 will be positive with respect to the center tap 134 and the terminal 133 ofjthat winding During this half cycle, the terminal 128 of the will be negative with respectto the center-tap 134. Very little current will flow in the switching circuit 99 because of the negative collector to base and emitter base voltage 'bias on the transistor 106. A large current, however, will flow through the switching circuit 98. The direction of this current flow will befrom the end terminal 128 of the winding 129 through the collector to base circuit of the transistor 104, which will conduct despite its negative collector bias because of its positive emitter bias, and through parallel combinations of the motor control winding 135 to the center tap of the winding 134 of the winding 129 and thecondenser 140 to the center tap 134. During the nexthalf cycle, the respective emitter and collector-biases will be reversed. Very little current will flow intheswitching circuit 99 because of thenegative collector to-base and emitter to 'base'bias voltages on the transistor 105. During this half cycle,

however, a large current will flow in the switchingcircuit 98. The direction of this current flow will be from the center tap 134 of the secondary winding 129, through the parallel combination of the motor control winding 135 and the condenser 140, through the collector to base circuit of the transistor 103, which will have a low impedance despite its negative collector bias because of its positive emitter bias, to the negative end terminal 128 of the secondary winding 129. Thus, when the control signal is 180 out of phase with the reference voltage, the switching circuit 98 will energize the motor control winding 135 with a 60 cycle alternating current which will lead the reference voltage by approximately 90.

From the foregoing it can be seen that the phase discriminating switching circuit 83 is operative to energize the rebalancing motor 84 for rotation in a direction dependent upon the phase relationship between the control signal and the reference voltage. Upon a change in the resistance of the temperature sensitive resistor 80, the Wheatstone bridge circuit 81 will be unbalanced and a voltage signal proportional in magnitude and phase to the direction and extent of the unbalance will appear between the junction point 95 and the sliding contact 92 on the slidewire resistor 87. Since the bridge circuit 81 is energized by the voltage across the conductors L the reference voltage, the "switching circuit 99 of the and L which voltage is the reference voltage for the phase sensitive switching circuit 83, this unbalance signal will be in phase or out of phase with this reference voltage depending upon the direction of the "bridge unbalance. The unbalance signal is amplified by the alternating current amplifier 82 and is applied across the primary winding 101 of the input transformer 102 of the phase sensitive switching circuit 83. The switching circuit, in turn, energizes the rebalancing motor 84, in accordance with the phase relationship between this signal and the reference voltage, driving it in the direction and to the extent necessary to rebalance the bridge 81 by repositioning the sliding contact 92 on the slidewire resistor 87 by means of the rebalancing mechanism 93.

While, in accordance with the provisions of'the statutes, there has been illustrated and described the best forms of this invention now known, it will be apparent to those skilled in the art that changes may be made in the forms of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of this invention may sometimes be used to advantage without a corresponding use of other features.

Having now described this invention, what is claimed as new and for which it is desired to secure Letters Patent, is:

1. A phase discriminating apparatus comprising, in combination, a pair of terminals'adapted to be connected to a source of alternating reference voltage, a :pair of transistors each having a collector, an emitter and a base, first circuit means serially connecting the collector of each of said transistors to a respective one of said terminals, the bases of :said transistors being directly connected together, current responsive means connected in circuit with the collector and base of said transistors, an input circuit adapted to be connected to a source of alternating control voltage having a reversible phase with respect to said reference voltage, and second circuit means connecting the emitter to base path of each of said transistors to said input circuit, said control voltage a transformer adapted to be connected to a source of alternating reference voltage, circuit means serially connecting the collector electrodes of :said transistors with the secondary winding of said transformer, the :bases of said transistors being directly connected together, a

single input circuit adapted to be connected to a source of alternating control voltage having a reversible phase with respect to said reference voltage, circuit means connecting the emitter and base electrodes of each of said transistors to said input circuit, and current responsive means connected in the collector to base current path of said transistors, said control voltage being effective when said transistors are so connected to control the collector to base impedance of said transistors and hence the flow of collector current.

3. A phase discriminating circuit, comprising in combination, a transformer having a secondary winding and a primary winding adapted to be connected across a source of alternating reference voltage, an input circuit adapted to be connected to a source of alternating signal voltage having a reversible phase with respect to said reference voltage, and two transistors each having a collector, an emitter, and a base, the emitter to base circuits of said transistors being connected in parallel to said input circuit, the collector to base circuits of said transistors being connected in series with a current sensitive load and the secondary Winding of said transformer.

4. Apparatus as specified in claim 3 wherein said current responsive load comprises a pair of polarized relays.

5. Apparatus as specified in claim 3 wherein said current responsive load comprises a filter and reversible di rect current motor.

6. A phase discriminating apparatus comprising in combination, a transformer, a secondary winding, and a primary winding adapted to be connected to a source of alternating reference voltage, a pair of transistors each having a collector, an emitter and a base, circuit means serially connecting the collector of one of said transistors to one end terminal of the secondary winding and the collector of the other transistor to the other end terminal of said secondary winding, a pair of relays one of which is connected between the collector and base of each of said transistors, a pair of input terminals adapted to be connected to a source of alternating control voltage having a reversible phase with respect to said reference voltage, circuit means connecting the emitter of each of said transistors to one of said pair of input terminals, and circuit means connecting the base of each of said transistors to the other of said pair of input terminals.

7. A phase discriminating apparatus comprising in combination, a transformer adapted to be connected to a source of alternating reference voltage, an input circuit adapted to be connected to a source of alternating control voltage having a reversible phase with respect to said reference voltage, a pair of transistors each having a collector, an emitter, and a base, the emitter to base circuit of each transistor being connected in parallel across said input circuit, the collector to base circuit of said transistors being connected in series with the secondary winding of said transformer, and a pair of relays, one of which is connected in parallel with the collector to base circuit of one of said transistors, and the other of which is connected in parallel with the collector to base circuit of the other of said transistors.

8. A phase discriminating circuit, comprising in combination, a two phase reversible induction motor having a power winding and a control winding, said power winding being adapted to be connected to a first source of alternating voltage, means for applying a voltage across said control winding which will energize said motor for rotation comprising a transformer having a primary winding adapted to be connected to said first voltage source and a center tapped secondary winding, two pairs of transistors each of said transistors in said pairs having a collector, an emitter, and a base, a first series circuit including the collector to base circuits of the transistors of one of said pairs, half of said transformer secondary winding and the motor control winding, a second series circuit including the collector to base circuits of the transistors of the other of said pairs, the other half of said secondary winding, and the motor control winding, an input circuit adapted to be connected to a second source of alternating voltage having a reversible phase in respect to said first voltage source, and means connecting the emitter to base circuits of said transistors to said input circuit.

9. A phase discriminating apparatus comprising in combination a pair of terminals adapted to be connected to a source of alternating reference voltage, an input circuit adapted to be connected to a source of alternating voltage having a reversible phase with respect to said reference voltage, a pair of transistors each having a collector, an emitter, and a base, first circuit means connecting the emitter to base current path of each of said transistors to said input circuit, second circuit means serially connecting the collectors of said transistors to said pair of terminals, respectively, said bases being directly connected together, and current responsive means connected to the collector to base path of said transistors.

10. A phase discriminating apparatus comprising, in combination, a pair of transistors each having a collector, an emitter and a base, said transistors having their bases directly connected together, a series circuit including said base connected transistors and an alternating reference voltage input means, said reference voltage input means having a pair of terminals connected, respectively, to the collectors of said pair of transistors, current responsive means connected in circuit with the collector to base path of said transistors, and a control signal input circuit for connection to a source of alternating control voltage having a reversible phase with respect to said reference voltage, said input circuit being connected to the emitter to base path of each of said pair of transistors, said control voltage being effective, when said transistors are so connected, to control the current flow through said current responsive means in accordance with the phase relationship between said control voltage and said reference voltage.

References Cited in the file of this patent UNITED STATES PATENTS 2,475,792 Wild et al Dec. 28, 1948 2,528,054, Harrison Oct. 31, 1950 2,529,490 Field Nov. 14, 1950 2,632,460 Wallace Sept. 15, 1953 2,653,282 Darling Sept. 22, 1953 2,698,392 Herman Dec. 28, 1954 2,774,021 Ehret Dec. 11, 1956 

